Graphical User Interface (GUI) Reading Guide - http://www.linux.org/threads/gui-reading-guide.6471/
Icon Theme Specification - http://www.freedesktop.org/wiki/Specifications/icon-theme-spec/
Icon Naming Specification - http://standards.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html
Icon Theme Specification (single page) - http://standards.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html
Tango Icon Library - http://tango.freedesktop.org/Tango_Icon_Library
Tango Icon Theme Guidelines - http://tango.freedesktop.org/Generic_Icon_Theme_Guidelines